Tuesday, 22 May 2012

Wednesday Weed: Mediterranean mustard

Brassica fruticulosa, Karori, Wellington

Mediterranean mustard (Brassica fruticulosa subsp. mauritanica) is a characteristic Wellington weed. It's common here, and on the nearby Kapiti coast, with a few collections from Palmerston North. The first published records, misidentified as B. integrifolia, were from 1957 (Webb et al. 1988). Plants had been collected a bit earlier than that, from Wellington and Paekakariki. It's tempting to speculate that this North African subspecies came here with returning soldiers after World War Two, but there's no evidence to support that speculation.

The uppermost leaves of the common mustards in New Zealand—cabbage (B. oleracea), rape (B. napus), and turnip (B. rapa)—all have lobes that wrap around the stem. Mediterranean mustard has narrow upper leaves that taper to slender stalks (second from right above). Its flowers are small and pale yellow, and its fruits are wrinkled around the seeds, no more than 35 mm long, and have a very short gynophore (a stalk above the petal and stamen scars and below the first seed).

Brassica fruticulosa at Roca Grosso, Catalonia

Brassica fruticulosa seems to have stronger resistance to insect pests such as aphids (Ellis & Farrell 1995) and root fly (Jensen et al. 2002) than the cultivated brassicas do. That suggests this species could be useful in breeding programs as a source of pest resistance in cultivated brassicas, but breeders would need to evaluate the results closely if the resistance is conferred by a toxic compound or a bitter taste, such as the glucosinolates that are found in these plants.

Brassica fruticulosa flowers, Northland, Wellington.

(Footnote: Just before this post went live, the all-time readership of Theobrominated was 9,993 page views, so one of the readers of this post is likely to be No. 10,000. No prizes, because I can't tell who you are.)

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(c) text and photographs copyright Phil Garnock-Jones and may not be used without permission.
I'm a botanist in New Zealand. Twitter handle: @Theobrominated. Retired from academia and now working part time as a researcher in plant taxonomy. The rest of my time I like to do the things on the list below.
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